Analysis on performance and test of a new type of ultra-high pressure pipe joint

Analysis as well as application of ultra-high pressure hydraulic system and elements has become a trend. The structure and operation principle of a new type of ultra-high pressure pipe joint is introduced. The structure of the new type of ultra-high pressure pipe joint is simple and is easy to be produced. The finite element model on two working conditions( preload condition with 30 N·m torque and static-loading condition with 70 MPa pressure) is built and computed. The width of contact area,the equivalent stress status,as well as the contact pressure status are plotted and analyzed. According to the national standard,test on air-tightness,blasting,and cyclic endurance is conducted and the results show that the new type of ultra-high pressure pipe joint has the sealability for ultra-high pressure up to 70 MPa,and the DN6 ultra-high pressure pipe joint can provide effective seal under70 MPa fluid pressure. The research can provide a thinking and method on designing ultra-high pressure pipe joint and push forward the development of ultra-high pressure hydraulic system.

Design and Strength Analysis of A Spherical Connector for Lifting Subsystem in Deep Sea Mining System

A flexible connector of lifting pipes in a deep sea mining system is designed. The buttress thread （ based on API standard） is used and foreign experience in connector design is referred to. With this kind of connector, the lifting pipe wiU only bear the axial force, free of moment. The strength of the connector is analyzed in detail, including the connecting strength of the buttress thread, the dynamic load of the pipe system, pressures inside and outside of the pipe, the lateral stress of the pipe wall and so on. Especially, a geometric model is built for 3-D contact stress analysis. The distribution graph of contact stress is presented. It is indicated that the strength of the spherical connector meets the demand.

Research of Pipe Made of Cu -Zn -Si Shape Memory Alloy to Internally Sprayed Pipe Connection in Connected Technology

The copper-based shape memory alloy pipe joint was applied in the field of oil pipelines jointing as well as installing. It has many advantages than anything. In the paper, the basic principle and connection influence factors of copper-based shape memory alloy pipe joint were described. Experimental results shows the copper-based shape memory alloy pipe joints can be used in oilfield oil pipeline connection and it can solve the inner pipe joint corrosion damage problem by welding.

INVESTIGATION ON BRITTLE FRACTUREPROPAGATION－ARRESTING CHARACTERISTICS OF STEEL PIPE

In order to study crack propagation-arresting characteristics of steel pipe construction, a new test installation was designed. The experiments of 20 steel pipes, pipes with longitudinally weld, pipes with circumferential weld and steel pipe with sleeve were conducted. The testing results indi- cated that circumferential weld in pipe with overrnatching weld had beneficial effect on crack prop- agation arrcsting propcrtics and the mechanical split sleeve can be used as crack arrester to prevent crack propagation.

Study on mechanical behaviors of double shoulder drill pipe joint thread

Double shoulder drill pipe joint(DSJ)is a novel thread structure which appears in recent years.Its strength reduced efficiently while the structure design is not appropriately,for the DSJ’s mechanical behaviors weren’t well studied.In this paper a 3D whole structure finite element model of DSJ was established based on the Principle of Virtual Work,and validated the model’s computing results by experimental results.The authors analyzed the stress and strain distribution with the 3D whole structure finite element model’s computing results under torque moment,compression force,tension load,and bend moment.And then acquired the DSJ’s mechanical behaviors under each load.The research works of this paper refer accordance to recognize and design the DSJ.

INTERFACIAL BEHAVIOR OF PIPE JOINTS UNDER TORSION LOADS

The interfacial behavior of pipe joints is studied in this paper. Firstly, through nonlinear fracture mechanics, the analytical expressions of interfacial shear stress and the load- displacement relationship at loaded end of pipe joints under torsion loads are obtained. Thus the shear stress propagation and the debonding process of the whole interface for different bond lengths can be predicted. Secondly, through the analytical solutions, the influences of different bond lengths on the load-displacement curve and the ultimate load are studied. The stress trans- fer mechanism, the interface crack propagation and the ductility behavior of the joints can be explained.

Experimental study of the separated joint of an underground pipeline rehabilitated by cured-in-place pipe

Reinforced concrete pipes(RCPs)were commonly used in older underground pipelines in Taiwan,China.However,their joints are prone to damage,including fracture and separation,from problems such as overloading,poor backfilling,and liquefaction.For the rehabilitation of such aged pipelines,trenchless methods are preferred to minimize the impact on transportation.The cured-in-place-pipe(CIPP)rehabilitation could be one of the most popular trenchless methods suitable for the cases with angular alignment and changing cross-section.However,according to the existing standards,no details are available on the performance of the rehabilitated parts of the damaged pipeline,including the effect of separated joint.This study designed and conducted laboratory testing on the composite pipe joint(the CIPP rehabilitated RCPs with a separated joint)with different scenarios,including radial and longitudinal loading tests.The radial test results indicated that,for a small separation distance,CIPP rehabilitation can restore the original function of a pipeline and improve its hoop strength.The longitudinal test revealed that the damage due to bending was controlled by the tensile strength of the liner material.The ultimate flexural strength decreased as the separation distance increased.However,pipelines may be subjected to additional loads due to flotation or subsidence,for which the longitudinal loading capacity is often the limiting parameter.For such conditions,it is necessary to confirm,by more research,whether the wall thickness is sufficient.

New design method of unequal taper thread(UTT)pairs and its application in API NC38 thread improvement

API standard threads are the most commonly used thread configurations for drill pipe joints in the petroleum industry.Recently with the increasing application of horizontal wells and extended-reach wells in drilling engineering,drill pipe joint threads are subjected to complex loads,and drill pipe joint thread breakage accidents occur frequently.The API NC38 threaded pair used in the SU36-8-4H2 well suffered a fracture accident.Macroscopic analysis found that the fracture sites were located near the root of the first engagement pin-thread where the stress was greatest.Therefore,it is necessary to find an alternative method to reduce the largest stress of NC38 threads.Then,a new design method of unequal taper thread(UTT)pairs is proposed that the taper of pin thread,slightly smaller than the taper of matched-box thread,is not equal to one of box-thread.In the UTT pairs of API NC38 thread,the taper of box thread is kept as the standard taper of 1:6,but the taper of pin thread is,respectively,1:6.1(UTT-I),1:6.2(UTT-Ⅱ),1:6.3(UTT-Ⅲ)and 1:6.4(UTT-IV).The 3D finite element models of four UTT pairs and one standard pair based on NC38 thread were developed,and the mechanical properties of five thread pairs bearing such typical working loads as torque,axial compression,axial tension,bending moment,internal and external pressure,were analyzed.The results show that four UTT pairs are superior to the standard pair of API NC38,and UTT-Ⅲ has the most performance in all of four UTT pairs.Compared with the standard pair of API NC38,UTT-Ⅲ pair can improve the bearing capacity such as torsion strength,compression strength,tensile strength,bending strength,strength against internal and external pressure,by 24.8%,13.2%,22%,9.99%and 14.2%,respectively.The new design method of UTT pair enhances the bearing capacity of API NC38 thread,and has been applied in Changqing Drilling Company of CNPC Chuanqing Drilling Engineering Company Limited.The UTT-thread pair method is not only applicable for API series threads to improve the connection performance,but also suitable for various non-API taper connection threads to promote existing working ability such as air tightness,stress corrosion resistance,fatigue resistance et al.